Stencil sheet and method of making same



Dec. 14, 1943. N, H, mm ETAL 2,337,012

STENCIL SHEETS AND METHOD OF MAKING SAME 7 Filed March 11, 1941 y a 0 m a m m r r H M 4 r p. 1 M W a i w y W m a lrl 8 n li I? Jm @Mm HM m MW EM- 2. m WW 0% 4| 4 T mmm g mm l m w W 1X m hm m w m I mm H H. a): r-. WM 1. fi m E h n m fill g d w H J 0 E w lNVENfORS C Mfi Z! I 0151/ ATTORNEYS Patented Dec. 14, 1943 UNITED STATES PATENT 1 OFFICE I 2.337.012 STENCIL' IAIIVVIIEETHOD OF linois Application March 11, 1941. Serial No. 882,690; 16 Claims. (01. 101-1283) This invention relates to stencil sheets and method of making same, and aims to provide a stencil sheet perfectly adapted both to stencilization with a stylus and to stencilization in a typewriter.

A stencil sheet for making a stencil for use in a duplicating machine consists of an open, porous, fibrous base having a displaceable coating filling the interstices of the base. A common base is yoshino .paper. The usual coating consists essentially of a binding agent and softening agents. The nature and more particularly the proportion of the two agents determine the physical characteristics of the coating, which must be such as to make it displaceable by pressure applied to the sheet.

In preparing duplicating stencils from stencil sheets, it is customary to use a stylus for drawing and signatures and the type of a typewriter for text. The pressure which a stencil receives from a stylus is very different from the blow which it receives in a typewriter. It has long been recognized that in order to be well adapted for stencilization with a stylus, a stencil sheet should have a coating which is soft and fluent, so that it may be readily displaced by drawing a stylus across the sheet. It has also been recognized that .the most satisfactory stencil sheets for stencilization in a typewriter are those which have a relatively hard coating, which, while readily displaceable by a blow of the type, is not soft and fluent enough to fill the type of the typewriter and thus necessitate frequent cleaning of the type. It has proved impossible heretofore to provide a stencil sheet with a coating which is both soft and fiuid enough to stencilize well with a stylus and hard enough to avoid this by providing a stencil sheet with a coating that when the sheet is struck by type on this side, it does not fill the type. The non-uniform coating is formed by the amalgamation of two compatible layers-a relatively hard layer located mostly within the confines of the base, and arelatively fluent layer located mostly at one side of the base.

Our method of making such a stencil sheet eonsists in first impregnating a porous base with a thin, fast-drying solution producing a relatively hard layer within the base. After this layer has nearly, but not completely, dried, the impregnated base is coated with a thicker, slowdrying solution which is compatible with the first solution. This leaves on one side of the base a relatively fluent layer. The two layers, being compatible, amalgamate by interpenetration, producing a unitary rather than a laminated coating. But, notwithstanding the amalgamation which eliminates any definite line of demarcation, the different physical characteristics of the two layers are retained at the two sides of the amalgamated coating.

In order that the two coating solutions may be compatible and may produce layers which amalgamate, it is essential that the binding agents in both solutions be soluble in the solvent used in the second solution. Most desirably the two solutions contain the same solvent and the same binding agent and compatible or identical softening agents.

In describing our invention in detail, we shall refer to the accompanying drawing in which Figs. 1 and 2 are diagrammatic cross-sections of a stencil sheet showing the effect of the two steps of our method. v In the drawing, l0 represents the base sheet consisting of fibers ll, projecting beyond the general surface of the sheet in the form of a fuzz I 2 which is easily discernible to the eye and to the touch.

The first step in making the stencil sheet consists in impregnating the base Ill with a first coating solution containing a binding agent, softening agents and a volatile solvent in which the l binding agent isdissolved. The proportion and nature of the softening agents is so adjusted that the solution will deposit a film or layer harder than an ordinary stencil coating, but soft enough to be displaced by a blow of the type in a typewriter. A large proportion Of volatile solvent is used so as to make the solution quick-drying.

- rapidly that the ends of the fibers forming the fuzz l2 still project from the upper surface of the sheet 10, so that after drying, this side of the sheet still has a slightly rough feel.- Thus, as seen in Fig. 1, the efiect of the first coating operation is to leave in the base a layer 20 of coating material, most of which is within the confines of the base. This layer extends from slightly outside the under surface of the sheet to which the solution was applied, to slightly inside theextreme upper surface of the sheet.

The softening agent of the solution is partially absorbed into the fibers ll of the base l0, so that the ratio of binding agent to softening agents in the material deposited between the fibers is somewhat higher than it was in the solution. This effect as well as the composition of the solution makes the layer 20 harder and less fiuent than an ordinary stencil coating.

Being almost wholly within the confines of the porous base sheet III, the layer 20 to some extent strengthens the fibrous sheet, acting in this respect as a sizing.

After the layer left in the base by the first coating operation is nearly dry but while it still contains suflicient solvent to be very soft, the second coating solution is applied to the under side of the base. This solution alsocontains a binding agent, softening agents and a solvent in which the binding agent is dissolved. The ingredients are adjusted so as to deposit a soft and fluent material, and only a moderate amount of solvent is used so that the second solution is thicker than the first solution and dries more sheet therefore meets the most rigid require-' ments both of a sheet. to be stencilized by a stylus and of a sheet to be stencilized in a typewriter.

The coating solutions used in carrying out our method may consist of the ingredients commonly used in stencil sheet coating. The compounding of such solutions so as to deposit films or layers of different degrees of softness is well understood in the stencil sheet art. To illustrate the scope of our invention, we give a few illustrative formulae of coating solutions which deposit films or EXAMPLE I First solution Parts by weight Nitrocellulose 300 Alcohol 8,300 Ether 10,900 Castor oil- 1,125 Stearic acid 250 Benzyl alcohol 100 Triacetin 150 slowly. The second solution leaves on the under surface of the base a layer 30 which is shown in first layer to the upper side of the base. As a result, the amalgamated coating retains the physical characteristics of the first layer at the upper side of the sheet and those of the second layer at the lower side. A further result is that no part of the complete amalgamated coating projects beyond the confines of the projecting fibers at the upper side of the sheet.

The fiuent character of the coating at its lower side and indeed throughout its main body, makes the stencil sheet ideally adapted to stencilization by a stylus. At the same time the hardness of the coating at the upper side of the sheet effectively prevents filling oi the type when the'type strikes this side of the sheet in stencilizing the sheet in a typewriter. This desirable result is also insured by the fact that no part of the coating projects beyond the fibers at the upper side of the sheet. The new stencil This is a thin, highly volatile solution which dries rapidly and produces a displaceable but relatively hard coating.

Second solution Parts by weight Nitrocellulose Alcohol 920 Ether 1,960 Amyl stearai 500 Color (pigment) 100 EXAMPLE II First solution Parts by weight Gelatin 100 Glycerol 20 Mineral oil 500 Water 5,000

Second solution Parts by weight Gelatin 200 Glycerol 50 Sulphonated oil Mineral oil 800 Wax 300 Pigment 300 Water 3,400

In this case, each bath contains the binding agent, gelatin, dissolved in the solvent, water.

While it is desirable to use the same binder in both solutions so as to insure a thorough amalgamation of the two layers, this is not ab-. solutely essential in the practice of the invention. Diflferent binding agents may be used in the two solutions provided that the solvent of the second solution is capable of dissolving both the binding agents. This is the case in the following examples:

EXAMPLE III First solution Parts by weight Nitrocellulose 300 Alcohol 8,300 Ether 10,900 Castor oil 1,125 Stearic acid 250 Benzyl alcohol 100 Triacetin 150 Second solution Parts by weight Gelatin 200 Glycerol -50 Sulphonated oil 150 Mineral oil 800 Wax 300 Pigment i 300 Glacial acetic acid 3,400

I ExmrLn IV First solution Parts by weight Gelatin 100 Glycerol 20 Mineral nil 500 Water 5,000

Second solution Parts by weight Nitrocellulose 120 Glacial acetic acid 2,880 Amyl stearate 500 Color (pigment) 100 What we claim is:

1. A stencil sheet adapted. to be made into a stencil by a typewriter or by a stylus and comprising a porous base having a unitary but nonuniform displaceable coating which is relatively hard at one side of the sheet and relatively soft and fluent at the other side.

2. A stencil sheet comprising a porous base having a unitary displaceable coating consisting of a binding agent and softening agents. the ratio of binding agent to softening agents being greater at one side of the sheet than at the other.

3. A stencil sheet comprising a porous base having a unitary displaceable coating consisting of a cellulose compound and softening agents, th ratio of cellulose compound to softening agents being greater at one side of the sheet than at the other.

4. A stencil sheet comprising a porous base having a unitary displaceable coating consisting of a protein and softening agents, the ratio of protein to softening agents being greater at one side of the sheet than at the other.

5. -A stencil sheet comprising a porous base having a unitary but non-uniform displaceable coating consisting of a cellulose compound, a protein and softening agents, which is relatively hard at one side of the sheet and relatively soft and fluent at the other side.

6. A stencil sheet comprising a porous paper base and a displaceable coating of nitrocellulose and softening agents impregnating said base and projecting beyond the fibers of the base at one side of the base only.

7. A stencil sheet comprising a porous fibrous base having a unitary d splaceable coating consisting of a relatively hard sizing layer and a relatively soft external layer, said layers being compatible and merging into one another.

8. A stencil sheet comprising a porous fibrous base having a unitary but non-uniform d splaceable coating consisting of a relatively hard sizing layer of binding agent and softening agents and a relatively soft external layer of the same binding agent and compatible softening agents, said layers merging into one another.

9. The method of making a stencil sheet which comprises successively applying to an open base of porous fibres a quick-drying solution containing binder and softener and a compatible slowdrying solution containing binder and softener.

10. The method of mak ng a stencil sheet which comprises successively applying to an open base of porous fibres two solutions each containing volatile solvent, binder and softener, the solution first applied containing a relatively large proportion of volatile solvent and the second solution containing a relatively small proportion of the same volatile solvent.

11. The method of making a stencil sheet which comprises successively applying to a porous base a coating solution so compounded as to deposit a. relatively hard type-impressible film and a compatible solution so compounded as to deposit a relatively soft and fluent type-impressi- 12. The method of making a stencil sheet which comprises impregnating an open base of porous fibres with a relatively thin solution of a binding agent containing softening agents, and thereafter coating one side of the impregnated base with a relatively thick solution of a binder containing softening agents, the solvent of the second solution being capable of dissolving the binder of the first solution.

13. The method of making a stencil sheet which comprises successively applying to an open base of porous fibres a fast-drying coating solution and a slow-drying coating solution, the two solutions containing the same binder and softeners dissolved in the same solvent.

14. The method of making a stencil sheet comprising successively applying to a porous base a solution of nitrocellulose in a relatively large amount of volatile solvent and 'a solution of nitrocellulose in a relatively small amount of volatile solvent, the first solution containing sufficient softening agent to produce a displaceable but relatively hard film, and the second solution containing sufiicient softening agent to produce a soft and fluent film.

15. A stencil sheet comprising a porous fibrous basehaving a unitary displaceable coating consisting of a sizing-layer and an external layer of different degrees of hardness, said layers being compatible and merging into one another.

16. The method of making a stencil sheet which comprises applying to an open base of porous fibres a quick-drying solution containing binder and softener; and, after said solution has partly dried in the base and before it has completely dried, applying a compatible slow-drying solution containing binder and softener.

NIELS HOLGER BJERG. ALBERT B. DICK, JR. 

